This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Background: Implantable cardioverter-defibrillators (ICDs) have become a standard tool of modern interventional cardiology. Many years of development have led to a well-accepted standard of practice for a large and ever-growing cohort of patients. However, despite the considerable level of clinical success, an increasingly large, diverse population of patients with ICDs has exposed some of the limitations of this clinical technology. We are currently seeing a conjunction of broader use of ICDs on a more diverse population, in terms of age, anatomy, and clinical indication. Likewise, there has been a surge of recent academic and industrial attention to the problem of lead failure. All of these factors require a simulation package for "personalized" patient-specific defibrillation modeling of broad visibility. Finally, we expect our tools to have the flexibility to accommodate novel lead designs, as well as the unprecedented ability to compute results in complex anatomical scenarios. Rationale: We propose to continue and deepen our work on defibrillation modeling in the human torso, with special emphasis on non-standard anatomies and non-standard lead configurations, in collaboration with pediatric cardiologists at Children's Hospital Boston and Stanford University, a leading researcher on mechanics of defibrillation at John's Hopkins University, and an adult interventional cardiologist at University of Utah. The goal is to take significant steps toward improving our understanding of robust and efficient defibrillation approaches that have the potential to impact clinical practice in this critically important area of device-based intervention. Questions: Current ICD designs have been suboptimal for many patients considered to be "successfully" treated, and inadequate for special patient populations and subcutaneous applications. However, because departure from established technologies is both high-risk and expensive, device design has been very conservative and basic implant strategies have changed little since the technology was introduced. Design &Methods: The scientific methods and objectives of the DBP are as follows: (1) Increase our ability to confidently predict, via use of a simulation tool, intrathoracic fields produced by variable designs and numbers of implanted electrodes in a variety of poses;(2) Increase our understanding of how myocardial fiber structure influences the effects of applied electric fields on the fibrillating heart;and (3) Develop design criteria for several specific classes of scenarios of interest, including pediatric ICD implantation and implantation in patients with residual broken leads.